Photoconductography employing absorbed metal ions



March 29, 1966 D. R. EASTMAN ETAL 3,242,858

PHOTOCONDUCTOGRAPHY EMPLOYING ABSORBED METAL IONS Filed June 27, 1961 l? I /0 F/g/ ABSORBED 2 MEML /0/V$ Fig. 2

ME 7A1. H YDROX/DE DONALD R. EASTMAN RAYMOND F REI THEL INVENTORS BY KMJM WWW ATTORNEYS United States Patent O 3,242,858 PHOTOCONDUCTOGRAPHY EMPLOYING ABSORBED METAL IONS Donald R. Eastman and Raymond F. Reithel, both of Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Filed June 27, 1961, Ser. No. 120,038 9 Claims. (Cl. 101149.4)

This is a continuation-impart of US. Serial No. 45,951 filed July 28, 1960, now abandoned.

This invention relates to electrolytic recording and particularly to photoconductography.

Photoconductography forms a complete image at one time or at least a non-uniform part of an image is distinguished from facsimile which at any one moment produces only a uniform clot. The present invention relates particularly to that form of photoconductography in which the final image is produced on a sheet separate from the photoconductive layer.

Cross reference is particularly made to the cofiled application Serial No. 45,940 of John W. Castle, Jr., entitled Photoconductography Employing Reducing Agents, which is the first item in the list given below. The Castle process is a direct positive one whereas the present process produces a positive from a negative.

Cross reference is made to the following series of applications filed July 28, 1960 concurrently with the application of which this is a continuation-in-part.

Serial No. 45,940, John W. Castle, Jr., Photoconductography Employing Reducing Agents.

Serial No. 45,941, Raymond F. Reithel, Photoconductolithography Employing Nickel Salts, now abandoned and continuation-in-part Serial No. 120,863, filed June 7, 1961, now Patent No. 3,106,157, issued October 8, 1963.

Serial No. 45,942, Raymond F. Reithel, Photoconductolithography Employing Magnesium Salts, now Patent No. 3,053,179, issued September 11, 1962.

Serial No. 45,943, Raymond F. Reithel, Photoconductography Employing Spongy Hydroxide Images, now abandoned and continuation-in-part Serial No. 120,035, filed June 27, 1961, now Patent No. 3,106,518, issued October 8, 1963.

Serial No. 45,944, Raymond F. Reithel, Method for Making Transfer Prints Using a Photoconductographic Process."

Serial No. 45,945, Raymond F. Reithel, Photoconductography Employing Manganese Compounds, now abandoned.

Serial No. 45,946, Raymond F. Reithel, Photoconductography Employing Molybdenum or Ferrous Oxide, now abandoned and continuation-in-part Serial No. 120,- 036, filed June 27, 1961, now Patent No. 3,106,156, issued October 8, 1963.

Serial No. 45,947, Raymond F. Reithel, Photoconductography Employing Cobaltous or Nickelous Hydroxide, now abandoned and continuation-impart Serial No. 120,037 filed June 27, 1961, now Patent No. 3,057,788, issued October 9, 1962.

Serial No. 45,948, Donald R. Eastman, Electrophotolithography.

Serial No. 45,949, Donald R. Eastman, Photoconductolithography Employing Hydrophobic Images, now Patent No. 3,152,969, issued October 13, 1964.

Serial No. 45,950, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Electrolytic Images to Harden or Soften Films, now Patent No. 3,106,516, issued October 8, 1963.

Serial No. 45,952, Donald R. Eastman and Raymond F. Reithel, Photoconductography Employing Spongy Images Containing Gelatin Hardeners, now Patent No. 3,106,517, issued October 8, 1963.

Serial No. 45,953, John J. Sagura, Photoconductography Employing Alkaline Dye Formation, now Patent No. 3,057,787, issued October 9, 1962.

Serial No. 45,954, John J. Sagura and James A. Van Allan, Photoconductography Employing Quaternary Salts," now Patent No. 3,178,362, issued April 13, 1965.

Serial No. 45,955, Franz Urbach and Nelson R. Nail, Uniform Photoconductographic Recording on Flexible Sheets, now abandoned.

Serial No. 45,956, Franz Urbach and Nelson R. Nail, High Constrast Photoconductographic Recording, now abandoned.

Serial No. 45,957, Nicholas L. Weeks, Photoconductography Involving Transfer of Gelatin, now abandoned.

Serial No. 45,958, Donald R. Eastman, Photoconductolithography Employing Rubeanates, now Patent No. 3,095,808, issued July 2, 1963.

Serial No. 45,959, Donald R. Eastman and Raymond F. Reithel, Electrolytic Recording with Organic Poly mers, now Patent No. 3,106,155, issued October 8, 1963.

Serial No. 46,034, Franz Urbach and Donald Pearlman, Electrolytic Recording, now abandoned.

Electrolytic facsimile systems are well known. Electrophotoconductography is described in detail in British 188,030 Von Bronk and British 464,112 Goldmann, modifications being described in British 789,309 Berchtold and Belgium 561,403, Johnson et al.

One object of the present invention is to provide a reliable inexpensive photoconductographic process in which one or more prints are produced from a single photoconductographic master on untreated paper or on paper which has received inexpensive pre-treatment.

Another object of the invention is to provide a form of photoconductography which yields prints of better contrast than is obtained in prior photoconductographic processes in which the final image is formed directly on a dye sensitized photoconductive layer.

One of the features of the present invention is the fact that the material deposited electrolytically as such need not become part of the final image and therefore, need not have any optical density itself. It is usually a hydrophilic material.

In all of the embodiments 'of the invention a metal hydroxide is deposited electrolytically accompanied by, or treated subsequently to absorb, metal ions. These metal ions are utilized in the subsequent step or steps to constitute, or to form complex salts which constitute, the final image material having optical density. That is, the ions are transferred to a receiving sheet which either contains or is subsequently treated with, a reagent to form the color pigment or metal deposit. Thus the electrodepositable material is selected for properties such as ease and uniformity of plating, without concern as to whether the material is visible or not. Metal hydroxides, particularly magnesium hydroxide, are found to have the highly desirable property of being easily and uniformly plated by photoconductography and of being able to absorb silver, nickel, ferrous or ferric ions suitable for reactions to form final prints.

Whether the relationship of the metal ions to the metal hydroxide is one of adsorption or absorption is open to discussion, but the distinction does not matter. The effect is probably similar to the manner in which water is absorbed by a sponge although the ionic character of the sorbed material gives it the appearance of adsorption. The terms absorbed and absorption are adopted here in the generic sense to cover the phenomenon whichever way it is considered.

When the hydroxide image is one which includes iron or nickel hydroxide, these appear to act as an additional source of iron or nickel ions, but the term absorbed is used to refer to all the available metal ions in the hydroxide image.

According to the invention, an image pattern is produced as variations in electrical conductivity in a photoconductive layer and this pattern is developed electrolytically either simultaneously with the exposure of the photoconductiye layer or promptly thereafter while the variations in photoconductivitypersist. The material electrodeposited onto the photoconductive layer, in accordance with the invention, is a metal hydroxide (e.g. magnesium hydroxide which term includes hydrated oxide of magnesium) which hydroxide is almost colorless and is barely visible, if at all, on the photoconductive layer.

The electro deposited material may be essentially (1) magnesium hydroxide alone or (2) a combination of magnesium hydroxide and either iron hydroxide or nickel hydroxide or (3) a combination of ('1) or (2). and iron ornickel salts to constitute a source of iron or nickel ions or the deposit may be simply (4) iron hydroxide or nickel hydroxide without the magnesium hydroxide. In each case involving iron (or nickel) hydroxide, iron (or nickel) ions are available. When magnesium hydroxide alone is; applied electrolytically, the invention requires a subsequent treatment with a silver, iron or nickel salt solution to provide silver, iron or nickel ions respectively which are; absorbed by the magnesium hydroxide. In such case the ions are absorbed by the metal hydroxide and are not absorbed by the areas of the photoconductive layer which are hydrophobic. Thus in all embodiments of the invention the first two steps (or single combined step) provide on the photocondu cti-ve layer a metal hydroxide image containing absorbed metal ions of silver, iron or nickel. The example in whichiron is present in the image and silver ions are applied is not very satisfactory but; all the other combinations are excellent.

The next stage of the process according to the inven.-. tion can also be performed in. twoseparate steps or simultaneously as a single step. The ions, are transferred to a receiving sheet which either has already been specially prepared to. contain, or is later treated with, a reagent which reacts-with the transferred: ions to form a material having optical density. For example silver ions can be transferred to a material containing. photographic developer so that the ions are reduced to metallic silver or containing a sulfide so. that black silver sulfide is formed or containing a, salt with which. thev silver ion reacts to form a more complex salt, which is colored. Similarly nickel, ferrous or ferric ions are known toreact with certain salts to. produce a pigment or dye and these salts can be incorporated in the receiving sheet.

In each of'these examples, the metal ion of silver, nickel or iron. can. be transferred to a receiving sheet not containing the reagent but which is later treated with the reagent to. produce the color. The receiving sheet with. or without the reagent may contain a solvent for the salt or other material generating the silver, nickel or iron ions to, assist the transfer of the ions to the receiving sheet.

Other objects and advantages of the present invention will be apparent from the accompanying drawings and from the examples given below. In the drawings:

FIG. 1 is a schematic flow chart illustrating the first stage of one embodiment of the invention.

FIG. 2 similarly illustrates an alternative first stage.

FIGS. 3 and 4 are respectively flow charts of forms which the second stage of the invention may take, FIG. 4v representing the preferred embodiment.

In FIG. 1 a transparent record 10 illuminated by a light source 11 is imaged by a lens 12 on a photoconductive layer i preferably of zinc oxide in suitable binder, carried on a conducting support 16. The arrows 17 and 18 indicate the relative motion of the transparency- 10,

and the sensitive layer 15 to permit the whole image to be exposed. This illustrates one common form of photoconductography. The other is equally applicable to the present invention and involves exposure of the whole photoconductive layer at one time while the layer is in an electrolytic bath so that development takes place simultaneously with exposure (see some of the cofiled applications mentioned above). However, as is known, zinc oxide retains its photoconductivity for a period of time after exposure which permits post exposure developm nt as shown in FIG. 1.

In the arrangement shown the exposed Zinc oxide is passed through an electrolytic bath consisting of a roller electrode 21 and a brush 2 0 applying the electrolyte to the layer. Electric current is provided by a source indicated schematically at 22 which causes the zinc oxide layer to act as the cathode.

The electrolyte in the brush 20 contains magnesium ions in the examples shown. It could contain nickel or iron ions or mixtures of these metal ions, as discussed in connection with FIG. 2-.

In FIG. 1 magnesium hydroxide is deposited at 23. corresponding to the exposed, and: hence conducting, areas of the zinc oxide layer 15. The unexposed areas do not receive any deposited image. Magnesium hydroxide is barely visible on the zinc oxide layer; it does; not matter for the purposes of the present invention whether it is visible or met. A metal hydroxide layer tends to be hydrophilic and the zinc oxide backgroundtends to be hydrophobic. In the example illustrated in FIG. 1-, the image 23 is then treated by a solution, applied by a brush 26, containing metal ions of silver, nickel or iron. The metal ions are adsorbed (or absorbed) as indicated at 27.

FIG. 2 differs from FIG. 1 in that the metal ions are available from the metal hydroxide itself or are applied with the metal hydroxide. That is, in FIG. 2 the electrolyte in the brush 31 contains nickel or ironions (nickel or iron salt in solution) which deposits as nickel or iron hydroxide. Alternatively it may contain both the nickel or iron ion and magnesium ion so that magnesium hydroxide isdeposited along with the iron or nickel ions and possibly iron ornickel hydroxide is also deosited. When nickel or ferrous hydroxide is all or part of the plated image, it acts as a source of metal ions or additional metal ions fortransfer. Again, thephotoconductographic proc-. ess illustrated in FIG. 2 can be performed simultaneously with the exposure as discussed above in connection with FIG. 1. In all cases, the image at the conclusionv of the steps illustrated in. FIGS. 1 and 2 is made. up. of a metal hydroxide with absorbed metal ions of silver, nickel or lI'OI'l.

In FIGS. 3 and 4 this metal ion image27; is-transfer-red to a receiving sheet and simultaneously or subsequently converted'to a material having optical density.

In FIG. 3- the ions 27 are transferred as shown at 35 to. the surface of the receiving sheet 36 by pressure between rollers 37. The transferred ions 35, are then treated; with a reducing or reacting solution in a brush 318 to form. a material 39 having optical. density.

The most preferred embodiment of the. invention is illustrated in- FIG. 4, in which both the transfer and color forming steps are performed substantially simultaneously. In this case, a sheet of paper 41 is-preparedin advance by coating with a surface layer 42' containing the reagent or reducing agent which causes the ions to form a coloring material. When the ionic metal image 27 is pressed into contact with the layer 42 by rollers 43, the ions are transferred to the layer 42 simultaneously (or immediately thereafter) form the complex salt, simple salt or, other material, 45 having optical density. A succession of such receiving sheets may be pressedinto contact with the ionic image 27 and thus several prints. can be made from a single ionic image.

was added to the above solution in some cases.

The following examples are described primarily with respect to FIG. 4. They are also applicable to FIG. 3 by having the color forming agent incorporated in the solution applied by the brushes 31 and 38 respectively instead of being incorporated in the receiving layer 42.

Example 1 Silver ions, absorbed by an imagewise distribution of electrolytically deposited magnesium hydroxide (or hydrated oxide) are transferred into the hydrophilic surface of a separate recording layer bearing a nucleating agent. Subsequent reduction of these silver ions to the metal yields a brown to black image in the recording layer.

A sheet of photoconductive, dye-sensitized zinc oxide material was exposed for 5 seconds to 400 foot candles tungsten radiation incident upon a high-contrast negative transparency in contact with the photoconductive surface and was then developed, electrolytically, with a viscose sponge wetted with an aqueous solution containing 0.8% by weight, magnesium nitrate hexahydrate. The print surface was then dried with an absorbent tissue which removed excess electrolyte from the non-image-bearing areas.

An aqueous solution of 5% by weight silver nitrate was then applied to the print surface, after which the surface was again dried by wiping with an absorbent tissue.

Silver ions, absorbed by the electrolytic image deposit (but rejected by the hydrophobic non-image-bearing areas) were then transferred by pressure-contact into the water-moistened hydrophilic surface of a recording layer (described in detail below) containing a nucleating agent.

Contact was maintained for seconds before separating the recording layer from the master.

The silver ions were then reduced chemically to metallic silver by bathing the print for 5 seconds in an aqueous solution of the following formula:

Percent (by weight) vHydroquinone 2 Phloroglucinol 0.5 Sodium sulfite 2 Sodium carbonated-sodium hydroxide to bring pH=10.0

cc. 5% by weight gelatin 50 Colloidal nickel sulfide (0.002 M in 2% gelatin) 0.7 Glycerol 1.5 formaldehyde Wetting agent To produce blue black tones rather than a brownish tone, 0.1 gram of standard photographic cold toner The coated layer was set in each case by chilling at a reduced temperature and then air dried at room temperature for several hours before use.

Example 2 Silver ions absorbed by an imagewise distribution of electrolytically deposited magnesium hydroxide (or hydrated oxide) are transferred into the hydrophilic surface of a separate recording layer which contains a nucleating agent and a chemical developer that reduces the transferred'silver ions to metallic silver during the transfer procedure, thereby eliminating a separate chemical development step after the transfer and also eliminating the necessity for washing the print after chemical development.

A piece of the photoconductive material was exposed, electrolytically developed, and the surface dried as in Example 1.

A 5% by weight, silver nitrate solution was applied and the print surface dried with an absorbent tissue.

Silver ions, absorbed by the magnesium hydroxide image-bearing areas, were transferred, by pressure contact, into a recording layer containing a nucleating agent and chemical developer. Contact was maintained for 40 seconds before separation of the recording layer from the master. A visible image had formed in the recording layer during the 40 sec. transfer time. By repeating the above procedure, application of another sheet of recording layer, etc., three good copies were obtained from this one master.

The recording layer was made in the following manner.

A baryta-coated white paper stock was overcoated, using a 0.005 in. aperture blade, with an aqueous solution of 5%, by weight, gelatin solution cc 50 Colloidal nickel sulfide (0.002 M in 2% gelatin) c 0.7 .2,S-dihydroxyphenylisothiouronium chloride g 0.5 Glycerol cc 1.5 40% formaldehyde cc 0.6

The coated layer was set by chilling at a reduced temperature and then air dried at room temperature for several hours before use.

Example 3 Silver ions, absorbed by an imagewise distribution of electrolytically deposited magnesium hydroxide (or hydrated oxide) are transferred into the hydrophilic surface of a separate recording layer containing sodium rhodizonate and react to form a brown-black inner complex in the recording layer.

A sheet of photoconductive material was exposed, electrlolytically developed, and then surface dried as in Examp e l.

A 5%, by weight, aqueous silver nitrate solution was applied and the print surface dried with an absorbent tissue.

Silver ions, absorbed by the magnesium hydroxide image-bearing areas, were transferred by pressure-contact into the water-moistened hydrophilic surface of a recording layer containing sodium rhodizonate (as described below). Contact was maintained for 20 seconds before separation of the recording layer. A visible image was formed during the 20 sec. transfer time. By repeating the transfer procedure, three copies were obtained from masters produced in this manner.

The recording layer for this system was made in the following manner.

A baryta-coated white paper stock was overcoated,

using a 0.003 in. aperture blade, with an aqueous solution of 5%, by weight, gelatin solution cc 50 Sodium rhodizonate g 0.1 Glycerine cc 1.5 40% formaldehyde cc 0.6

The coated layer was set by chilling at a reduced temperature and then air dried at room temperature for several hours before use.

Example 4 Silver ions, absorbed by an imagewise distribution of electrolytically deposited magnesium hydroxide (or hydrated oxide) are transferred into the hydrophilic surface of a recording layer containing zinc sulfide which reacts an absorbent tissue.

trolytically developed, and then surface dried as in Example 1.

A by weight aqueous silver nitrate solution was applied and the print surface dried with an absorbent tissue.

Silver ions, absorbed by the magnesium hydroxide image-bearing areas, were transferred by pressure-contact into the water-moistened hydrophilic sufrace of a recording layer containing finely divided zinc sulfide (as described below). Contact was maintained for 30 seconds. A visible image was formed on the recording layer during the transfer time. By repeating the transfer procedure, two copies could be made from a master produced in this manner.

The recording layer for this system was made in the following manner.

A baryta-coated white paper stock was overcoated, using a 0.005 in. aperture blade with an aqueous dispersion comprised of 6 grams zinc sulfide in 20 cc. of 0.5% gelatin solution, roller milled for 4 hours in a glass jar containing a single stainless steel roller, to which was added a solution made by combining:

cc. 10%, by weight, gelatin solution Glycerol 1.5 40% formaldehyde 0.6 Ethyl alcohol 2 The coating was set by chilling, then air dried at room temperature for several hours before use.

Example 5 Nickel ions, absorbed in an electrolytically deposited metal hydroxide (or hydrated oxide) are transferred into the hydrophilic surface of a separate recording layer containing alcohol solubilized dithiooximide which react to form the reddish-blue-colored nickel rubeanate.

A sheet of the photoconductive material was exposed for 2 seconds to 400 ft. candle tungsten radiation incident upon a high contrast negative transparency in contact with the photoconductive surface and then electrolytically developed as in Example 1 with an aqueous solution containing 1% by weight magnesium sulfate and 1% by weight nickel acetate. The surface was then dried with In this case the metal "hydroxide is electrodeposited and at the same time it absorbs nickel ions; the metal hydroxide is magnesium and/or nickel hydroxide.

Nickel ions, absorbed by the metallic hydroxide deposit of nickel and/or magnesium hydroxide, were transferred by pressure-contact into the water-moistened hydrophilic surface of a separate recording layercontaining alcohol-solubilized dithiooximide (described below). Contact was-maintained for 20 seconds. A reddish-blue image was formed during the transfer time. Repetition of the transferprocedure produced six prints from a single master made in this manner.

The recording layer was made in the following manner:

Dithiooximide (dissolved in cc. ethyl alcohol) g 0.5 10% by weight gelatin solution cc 50 Wetting agent cc 1 The above solution was coated on a baryta-coated white paper stock with a 0.005 in. aperture blade, set by chilling at a reduced temperature and then air dried at room temperature for several hours before use.

Example 6 Nickel ions, absorbed in an electrolytically deposited metal hydroxide, are transferred into the hydrophilic surface of a separate recording layer containing alcoholsolubilized dimethylglyoxime and reacts to form the reddish-colored nickel dimethylglyoxime.

A sheet of the photoconductive material was exposed for 5 seconds to 400 foot candle tungsten radiation incident upon a high contrast negative transparency in contact with the photoconductive surface and then electrolytically developed, as in Example 1, with an aqueous solution containing 0.25% by weight magnesium nitrate hexahydrate and 0.75%, by weight, nickel sulfate hexahydrate. After development the surface was dried with an absorbent tissue. Again, nickel ions are absorbed in nickel hydroxide or magnesium hydroxide as it is deposited.

From this master, threesuccessive prints were made by pressure-contacting the master surface with the Watermoistened hydrophilic surface of a separate recording layer containing the alcohol-solubilized dimethylglyoxime.

The recording layer was made by flow-coating the following solution on a 'baryta-coated white paper stock.

Dimethylglyoxime (in cc. 2 methoxyethanol) -gram 1.0

Example 7 Ferrous and/or ferric ions, absorbed in an electrolytically deposited metal hydroxide v(or hydrous oxide), are transferred into the hydrophilic surface of a separate recording layer containing 6,7-dihydroxy-2-naphthalenesulfonic acid sodium salt, which react to form a relatively stable, reddish-brown-colored complex.

A sheet of the photoconductive material was exposed for 5 seconds to 400 foot candle tungsten radiation incident upon a high contrast negative transparency in contact with the photo-conductor surface and then electrolytically developed as in Example 1 with an aqueous solution containing 0.75% by weight of ferrous sulfate heptahydrate plus 0.5% by weight of magnesium nitrate hexahydrate. After this electrolytic development, which deposited an image of metal hydroxide with absorbed ferrous ions, the photoconductor surface was dried with an absorbent tissue.

From this master, twelve successive prints of fairly uniform quality and image density were made by rolling into contact with it the recording'layer surface moistened with 0.4% ammonium chloride solution and containing 6,7-dihydroxy-f2-naphthalenesulfonic acid sodium salt. Five seconds reaction time in contact with the master was allowed for each print. The ammonium :chloride acts as a solvent for ferrous hydroxide and thus enhances .the transfer of the latter.

The recording layer was made by coating the following solution on a baryta-coated white paper stock using a 0.005 in..aperture blade.

10% by weightgelatin solution cc 5 Methyl alcohol cc 35 -6,7-dihydroxy 2 naphthalenesulfonic acid sodium salt g 1.0

The coating was air dried at room temperature before use.

Example 8 Ferrous ions, absorbed in an electrolytically deposited metal hydroxide, are transferred into the hydrophilic surface of a separate recording layer containing potassium ferricyanide which reacts to form the blue product, Turnbulls Blue.

A sheet of the photoconductive material was exposed for '5 seconds to 400 ft. candle tungsten radiation incident upon a high contrast negative transparency in contact with the photoconductive surface and then electrolytically dcvelopedwith an aqueous solution containing 0.75% by weight of ferrous sulfate hepta-hydrate plus 0.5% 'by weight of magnesium nitrate hexahydrate. It is believed that the image is ferrous hydroxide and magnesium hydroxide with absorbed ferrous and ferric ions. After electrolytic development the photoconductorsurface was dried with an absorbent tissue.

Ferrous and/or ferric ions, absorbed .by the metal hydroxide and/or hydrated oxide image-bearing areas,

were transferred by pressure-contact into the watermoistened hydrophilic surface of a recording layer containing potassium ferricyanide. Contact was maintained for 30 seconds before separation of the recording layer from the master. A blue image, consisting of Turnbulls Blue, was formed in the recording layer. By repeating the transfer procedure, three successive prints of fairly uniform quality and image density were obtained from masters produced in this manner.

The recording layer for this system was made in the following manner:

A baryta-coated white paper stock was overcoated, using a 0.005 inch aperture blade with an aqueous solution of by Weight gelatin solution cc 50 Potassium ferricyanide g 0.5 Glycerine cc 1.5 40% formaldehyde cc 0.6

The coated layer was set by chilling at a reduced temperature and then air dried at room temperature for several hours before use.

Example 9 Ferrous and/or ferric ions, absorbed in an electrolytically deposited metal hydroxide (or hydrated oxide), are transferred into the hydrophilic surface of a separate recording layer containing gallic acid which react to form the blue-black iron gallate complex.

A sheet of the photoconductive material was exposed for 5 seconds to 400 foot candle tungsten radiation incident upon a high contrast negative transparency in contact with the photoconductor surface and then electrolytically developed as in Example 1 with an aqueous solution containing 0.75% by weight of ferrous sulfate heptahydrate plus 0.5% by weight of magnesium nitrate hexahydrate. After the electrolytic development was terminated, the photoconductor surface was dried with an absorbent tissue.

From this master, three successive prints of decreasing image density were made by rolling it into contact with a water-moistened hydrophilic surface of a recording layer containing gallic acid. Ten seconds reaction time in contact with the master was allowed for each print.

The recording layer was made in the following manner:

A baryta-coated paper support was overcoated, using a 0.005 inch aperture blade with a solution of 10% by weight gelatin solution cc 5 Gallic acid g 1.0

Methyl alcohol cc 35 Distilled water cc 10 by weight sodium hydroxide solution cc 0.4 The coating was air dried at room temperature for several hours before use.

In the electrolytic processes described in this and the various copending applications referred to above there are in general no critical or special limits on the potential applied or the concentration of the salts in the electrolyte. Of course the potential cannot be so high that it causes electrical breakdown of the photoconductive layer and cannot be so low that there is no appreciable electrolytic effect within a reasonable time. Similarly the concentration of the salt in the electrolyte cannot be above saturation or cannot be so low that there is no appreciable deposit during a reasonable period of electrolytic action.

However, in the case of nickel salts when the hydroxide of the metal is to be deposited, there is a minimum voltage (about 30 volts) and a maximum concentration (about 3%), since at lower voltage or at higher concentrations the metal itself, without a useful amount of the hydroxide, tends to deposit. All of the examples involving nickel given in the present series of apph'cations do have concentrations below 3% and voltages above 30 volts so that useful amounts of hydroxide are deposited. Whether metal is also deposited is of little concern.

Nickel hydroxide is much more hydrophilic than nickel metal and is more absorbent (spongy) than nickel itself. Also nickel metal images do not have satisfactory optical density whereas the deposit of nickelous hydroxide and conversion to nickelic oxide does give a high density. These various effects are involved in different applications of this present series. Also any :concentration above 3% not only gives adverse effects, but adds to the cost of whichever process is involved.

As with other materials, the upper limit on the voltage is that imposed by electrical breakdown and the lower limit on concentration of nickel salts is merely that amount which gives an appreciable deposit in a reasonable time under the voltage available. This lower limit is obviously not critical.

Cobalt and iron salts behave somewhat like the nickel salt-s. At higher concentrations and lower voltages, the ratio of metal (or at least of a metalliclike deposit which appears) to hydroxide increases. Cobalt hydroxide images appear light blue and ferrous hydroxide images appear olive green. When the process involves producing cobalt oxide (which has a good density compared to cobalt metal images) the concentration should be below 3% and the voltage above 30 v. (as in the case of nickel). Iron is not used in such processes since ferric oxide and hydroxide are light colored. When the process involves sponginess or physical absorption by the image, [both iron and :cobalt must again be used in con centrations below 3% and at voltages above 30 v. since the hydroxide images are much more absorptive than the metal images. When the process involves the hydrophilicity of the image, 30 v. is still the lower useful limit and the preferred concentrations are still below 3% although higher concentrations of iron salts and particularly of cobalt salts still give useful results because the metal images themselves have considerable hydrophilicity although not nearly as good as that of the corresponding hydroxides. Finally, when the process involves reduction (nickel hydroxide images by themselves are never used in reducing processes) the limits on con- .centration and voltages are only the general ones (i.e. up to saturation and between the voltage which gives an appreciable deposit in a reasonable time and the voltages which cause breakdown) because the metal image itself is reducing for both cobalt and iron.

While several preferred examples of the invention have been given herein, it should be understood that the invention is not limited to such examples but is of the scope of the appended claims.

We claim:

1. In a photoconductographic process for producing from a negative transparency, positive prints on paper, in which process an image pattern of variations in electrical conductivity is produced in a hydrophobic photoconductive layer, the steps comprising forming on the photoconductive layer by passing current through the layer distributed in accordance with said pattern and by the presence of a solution containing magnesium ions, an image comprising magnesium hydroxide, applying to the deposited hydroxide image a solution containing ions of a metal selected from the group consisting of silver, nickel and iron, transferring the metal ions by pressure from the metal hydroxide image to the surface of a receiving sheet and converting said ions to a material having optical density.

2. A process according to claim 1 in which the re ceiving sheet contains a reagent for converting the ions to a material with optical density at the time the ions are transferred to the receiving sheet.

3. A process according to claim 1 in which the absorbed and then transferred ions are silver ions which are reduced to metallic silver to form the material having optical density.

4. A process according to claim 1 in which said transferring and converting steps are substantially simultaneous by having a color forming reagent which reacts with the ions to fionrn said material having optical density, in the receiving sheet at the [time of said transferring.

5. A process according to claim 1 in which the transferred ions are silver ions and in which said converting results firom reaction of the silver ions with a salt selected from the group consisting of sodium rhodizronate and metal sulfides.

:6. A process according to claim 1 in which the :trans- [ferred ions are nickel ions and in which said converting results from reacting the nickel ions with an alcohol solubilized compound selected from the group consisting of: dithiooximide and .dimethylglyoxime.

7. A process according to claim -1 in the transferred ions .are iron ions and in which said converting results from reacting the iron ions with .a compound selected from the group consisting of a6,7-.,dih-ydroxy-2- naphthalene sulfonic acid alkali salt and gallic acid to form the material having optical density.

8. A process according to claim 1 in which the transferred ions are ferrous ions and in which said converting results firorn reacting the ferrous ions with potassium ferricyanide to form Turnbulls Blue.

9. A process according to claim 1 in which the transferred ions are iron ions and in which the receiving sheet contains ammonium chloride.

References Cited by the Examiner U TED S ATES ATE TS 2,038,486 4/1936 G las -101426 2,316,340 4/1943 Kohn 101-426 2,663,656 12/1953 Miller et a1. 101-426 2,936,707 5/1960 Maguire et a1. 101426 3,011,963 12/1961 Johnson et a1. 101149.2

DAVID KLEIN, Primary Examiner. 

1. IN A PHOTOCONDUCTOGRAPHIC PROCESS FOR PRODUCING FROM A NEGATIVE TRANSPARENCY, POSITIVE PRINTS ON PAPER, IN WHICH PROCESS AN IMAGE PATTERN OF VARIATIONS IN ELECTRICAL CONDUCTIVITY IS PRODUCED IN A HYDROPHOBIC PHOTCONDUCTIVE LAYER, THE STEPS COMPRISING FORMING ON THE PHOTOCONDUCTIVE LAYER BY PASSING CURRENT THROUGH THE LAYER DISTRIBUTED IN ACCORDANCE WITH SAID PATTERN AND BY THE PRESENCE OF A SOLUTION CONTAINING MAGNESIUM IONS, AN IMAGE COMPRISING MAGNESIUM HYDROXIDE, APPLYING TO THE DEPOSITED HYDROXIDE IMAGE A SOLUTION CONTAINING IONS OF A METAL SELECTED FROM THE GROUP CONSISTING OF SILVER, NICKEL AND IRON, TRANSFERRING THE METAL IONS BY PRESSURE FROM THE METAL HYDROXIDE IMAGE TO THE SURFACE OF A RECEIVING SHEET AND CONVERTING SAID IONS TO A MATERIAL HAVING OPTICAL DENSITY. 